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Abstract:

An object of the invention is to make it possible to introduce exhaust
gas 3 into a post-treatment unit such as selective reduction catalyst 6
through turnabout, with distribution of flow of the exhaust gas 3 being
uniformized. Disclosed is an exhaust emission control device with a
selective reduction catalyst 6 (post-treatment unit) for depuration of
the exhaust gas 3 through passing therethrough being arranged in an
exhaust system, a layout being applied which introduces the exhaust gas 3
into the selective reduction catalyst 6 through turnabout. An
introductory part 14 is provided which encircles an inlet end of the
selective reduction catalyst 6 and guides the exhaust gas 3 through the
exhaust inlet port 13 from a direction substantially perpendicular to an
axis of the selective reduction catalyst 6. The introduction part 14 is
formed with a depression 15 (first depression) cambered away from the
inlet end of the selective reduction catalyst 6 and approaching toward
the inlet end of the selective reduction catalyst 6 as it extends away
from the exhaust inlet port 13 into an introduction direction of the
exhaust gas 3.

Claims:

1. An exhaust emission control device wherein a post-treatment unit for
depuration of exhaust gas passing therethrough is arranged in an exhaust
system, a layout being applied which introduces the exhaust gas into the
post-treatment unit through turnabout, comprising an introductory part
which encircles an inlet end of the post-treatment unit and which
introduces the exhaust gas through an exhaust inlet port from a direction
substantially perpendicular to an axis of said post-treatment unit, said
introductory part being formed with a first depression which is cambered
away from the inlet end of the post-treatment unit and which approaches
the inlet end of the post-treatment unit as the first depression extends
away from the exhaust inlet port into an introduction direction of the
exhaust gas.

2. An exhaust emission control device as claimed in claim 1, wherein the
exhaust passage connected to the exhaust inlet port of the introductory
part extends to be directed toward an outlet side of the post-treatment
unit, and a second depression is formed just in front of a curved portion
constituted by the exhaust passage and the exhaust inlet port so as to
guide the flow of the exhaust gas inwardly of the turning direction
toward outward.

Description:

TECHNICAL FIELD

[0001] The present invention relates to an exhaust emission control
device.

BACKGROUND ART

[0002] It has been recently proposed that a particulate filter for
capturing of particulates in exhaust gas is incorporated in an exhaust
pipe and a selective reduction catalyst capable of selectively reacting
NOx with ammonia even in the presence of oxygen is arranged
downstream of the particulate filter, urea water as reducing agent being
added between the reduction catalyst and the particulate filter, thereby
attaining reduction of both the particulates and NOx.

[0003] Such addition of the urea water to the selective reduction catalyst
is conducted between the particulate filter and the selective reduction
catalyst. Thus, in order to ensure sufficient reaction time for pyrolysis
of the urea water added to the exhaust gas into ammonia and carbon
dioxide gas, it is necessary to prolong a distance between a urea water
added position and the selective reduction catalyst. However, such
arrangement of the particulate filter and the selective reduction
catalyst substantially spaced apart from each other will extremely impair
the mountability on a vehicle.

[0004] In order to overcome this, a compact, exhaust emission control
device as shown in FIGS. 1 and 2 has been proposed by one of the
applicants as Japanese patent application No. 2007-29923. In the exhaust
emission control device of the prior application shown, incorporated in
an exhaust pipe 4 through which exhaust gas 3 flows from a diesel engine
1 via an exhaust manifold 2 is a particulate filter 5 housed in a casing
7 to capture particulates in the exhaust gas 3; arranged downstream of
and in parallel with the particulate filter 5 and housed in a casing 8 is
a selective reduction catalyst 6 having a property capable of selectively
reacting NOx with ammonia even in the presence of oxygen. An outlet
end of the particulate filter 5 is connected to an inlet end of the
selective reduction catalyst 6 through an S-shaped communication passage
9 such that the exhaust gas 3 discharged through the outlet end of the
particulate filter 5 is antithetically turned about into the inlet end of
the adjacent selective reduction catalyst 6.

[0005] As shown in FIG. 2 which shows substantial parts in enlarged scale,
the communication passage 9 is the S-shaped structure comprising a gas
gathering chamber 9A which encircles the outlet end of the particulate
filter 5 to gather the exhaust gas 3 through substantially perpendicular
turnabout of the gas just discharged from the outlet end of the
particulate filter 5, a mixing pipe 9B which extracts the gathered
exhaust gas 3 from the chamber 9A in a direction antithetical to that of
the exhaust gas flow in the filter 5 and which is provided with urea
water addition means 10 at an axis of an inlet end of the mixing pipe and
a gas dispersing chamber 9C which encircles the inlet end of the
selective reduction catalyst 6 so as to disperse the gas 3 guided by the
mixing pipe 9B through substantially perpendicular turnabout into the
inlet end of the selective reduction catalyst 6.

[0006] Arranged in the casing 7 and in front of the particulate filter 5
is an oxidation catalyst 11 for oxidization treatment of unburned fuel in
the exhaust gas 3, and arranged in the casing 8 and behind the selective
reduction catalyst 6 is an ammonia reducing catalyst 12 for oxidization
treatment of surplus ammonia.

[0007] With the exhaust emission control device thus constructed,
particulates in the exhaust gas 3 are captured by the particulate filter
5. Intermediately of the mixing pipe 9B downstream of the filter, the
urea water is added into the exhaust gas 3 by the urea water addition
means 10 and is decomposed into ammonia and carbon dioxide gas; on the
selective reduction catalyst 6, NOx in the exhaust gas 3 is
favorably reduced and depurated by the ammonia. As a result, both the
particulates and NOx in the exhaust gas 3 are reduced.

[0008] In this situation, the exhaust gas 3 from the outlet end of the
particulate filter 5 is introduced into the inlet end of the adjacent
selective reduction catalyst 6 through antithetical turnabout by the
communication passage 9, which ensures a long distance between the urea
water added position intermediately of the communication passage 9 and
the selective reduction catalyst 6 and facilitates mixing of the urea
water with the exhaust gas 3 due to the antithetical turnabout of and
thus turbulence of the exhaust gas flow, resulting in ensuring sufficient
reaction time for production of ammonia from the urea water.

[0009] Moreover, the particulate filter 5 is arranged in parallel with the
selective reduction catalyst 6 and the communication passage 9 is
arranged along and between the filter 5 and the catalyst 6, so that the
whole structure is compact in size to substantially improve the
mountability on a vehicle.

[0010] As a prior art literature pertinent to the invention, there is, for
example, the following Patent Literature 1.

[0011] [Patent Literature 1] JP 2005-155404A

SUMMARY OF INVENTION

Technical Problems

[0012] Even though the applied structure as shown in FIGS. 1 and 2 may
ensure sufficient reaction time of urea water into ammonia, it is feared
that the layout applied for introduction of the exhaust gas into the
selective reduction catalyst through turnabout may cause the exhaust gas
flow to be biased outwardly of a turning direction upon the turnabout; as
a result, the exhaust gas may be nonuniformly introduced into the
selective reduction catalyst, resulting in failure of sufficient
bringing-out of the catalytic ability to be inherently exerted.

[0013] It would be possible to suppress the above-mentioned biased exhaust
gas flow by turning about the exhaust gas at a position sufficiently away
from the inlet end of the selective reduction catalyst to introduce the
exhaust gas axially of the selective reduction catalyst. However, it
would preposterously resulting in deterioration in mountability.

[0014] It may be also conceivable that a dispersion plate is arranged on
an inlet side of the selective reduction catalyst for facilitation of
uniformalized flow. However, in the situation of the selective reduction
catalyst with the urea water being used as reducing agent as illustrated,
shielding of the flow by any resistive body such as a dispersion plate
after addition of the urea water may bring about corrosion of misty, not
completely ammonized urea water on the resistive body to induce
deposition of urea. Therefore, intervention by the dispersion plate is to
be avoided as much as possible.

[0015] The invention was made in view of the above and has its object to
attain introduction of exhaust gas through turnabout into a
post-treatment unit such as a selective reduction catalyst with
uniformized flow distribution of the exhaust gas.

Solution to Problems

[0016] The invention is directed to an exhaust emission control device
wherein a post-treatment unit for depuration of exhaust gas passing
therethrough is arranged in an exhaust system, a layout being applied
which introduces the exhaust gas into the post-treatment unit through
turnabout, characterized by comprising an introductory part which
encircles an inlet end of the post-treatment unit and which introduces
the exhaust gas through an exhaust inlet port from a direction
substantially perpendicular to an axis of said post-treatment unit, said
introductory part being formed with a first depression which is cambered
away from the inlet end of the post-treatment unit and which approaches
the inlet end of the post-treatment unit as the first depression extends
away from the exhaust inlet port into an introduction direction of the
exhaust gas.

[0017] Thus, when the exhaust gas introduced through the exhaust inlet
port from the direction substantially perpendicular to the axis of the
post-treatment unit into the introductory part flows axially of the
post-treatment unit through turnabout, the flow of the exhaust gas
directed outwardly of a turning direction thereof is suppressed by the
first depression and that of the exhaust gas directed inwardly of the
turning direction is induced so that the tendency of relatively much
exhaust gas flow biased outwardly of the turning direction is rectified
to uniformize distribution of the exhaust gas flow into the
post-treatment unit.

[0018] Moreover, it is preferable in the invention that the exhaust
passage connected to the exhaust inlet port of the introductory part
extends to be directed toward an outlet side of the post-treatment unit,
and a second depression is formed just in front of a curved portion
constituted by the exhaust passage and the exhaust inlet port so as to
guide the flow of the exhaust gas inwardly of the turning direction
toward outward.

[0019] Thus, for example, for a case where center-to-center distance
between the post-treatment unit and the exhaust passage upstream of the
exhaust inlet port is fixed and unchangeable due to layout restrictions,
the second depression causes a portion of the exhaust passage inwardly of
the turning direction once directed outward at a position just in front
of the curved portion so that a curvature of the curved portion can be
reduced for alleviation of pace of curving, resulting in guidance of the
exhaust gas flow into the exhaust inlet port in a smooth manner as much
as possible.

ADVANTAGEOUS EFFECTS OF INVENTION

[0020] An exhaust emission control device of the invention can attain
various effects and advantages as mentioned below.

(I) The exhaust gas can be introduced through the turnabout into the
post-treatment unit such as a selective reduction catalyst with
uniformized distribution of the exhaust gas, so that the whole volume of
the post-treatment unit can be effectively utilized for sufficient
bringing-out of the exhaust depuration ability to be inherently exerted.
(II) When the exhaust passage connected to the exhaust inlet port of the
introductory part extends to be directed toward the outlet side of the
post-treatment unit and the second depression is formed just in front of
the curved portion constituted by the exhaust passage and exhaust inlet
port so as to guide the flow of the exhaust gas inwardly of the turning
direction toward outside, the curvature of the curved portion constituted
by the exhaust passage and exhaust inlet port can be reduced for
alleviation of pace of curving, resulting in guidance of the exhaust gas
flow into the exhaust inlet port in a smooth manner as much as possible.
As a result, the tendency of relatively much exhaust gas biased outwardly
of the turning direction can be further rectified and substantial
increase in pressure loss due to the turnabout of the exhaust gas can be
also prevented.

[0023]FIG. 3 is a sectional view showing an embodiment of the invention;
and

[0024] FIG. 4 is a view looking in the direction of arrows IV in FIG. 3.

REFERENCE SIGNS LIST

[0025] 3 exhaust gas

[0026] 4 exhaust pipe

[0027] 6 selective reduction catalyst (post-treatment unit)

[0028] 13 exhaust inlet port

[0029] 14 introductory part

[0030] 15 depression (first depression)

[0031] 16 mixing pipe (exhaust passage)

[0032] 17 depression (second depression)

DESCRIPTION OF EMBODIMENT

[0033] An embodiment of the invention will be described in conjunction
with the drawings.

[0034] FIGS. 3 and 4 show the embodiment directed to an exhaust emission
control device substantially similar to that shown in FIGS. 1 and 2.
Replaced for the gas dispersing chamber 9C as a downstream portion of the
communication passage 9 is an introductory part 14 which encircles an
inlet end of a selective reduction catalyst 6 to guide exhaust gas 3 from
a direction substantially perpendicular to an axis of the selective
reduction catalyst 6 through an exhaust inlet port 13. The introductory
part 14 has a depression 15 (first depression) which is cumbered away
from the inlet end of the selective reduction catalyst 6 and which
approaches toward the inlet end of the selective reduction catalyst 6 as
it extends away from the exhaust inlet port 13 toward the introduction
direction of the exhaust gas.

[0035] A mixing pipe 16 (exhaust passage) extending to an inlet side of
the selective reduction catalyst 6 is integrally formed with the exhaust
inlet port 13 at the introductory part 14. Formed just in front of a
curved portion provided by the mixing pipe 16 and the exhaust inlet port
13 is a depression 17 (second depression) which guides the exhaust gas
flowing inwardly of the turning direction to outward.

[0036] The portion of the mixing pipe 16 formed with the depression 17 is
vertically expanded in cross section as shown in FIG. 4 so that the
cross-sectional area of the passage do not greatly change before and
after the depression 17.

[0037] When it is thus constructed, the exhaust gas 3 introduced into the
introductory part 14 through the exhaust inlet port 13 from the direction
substantially perpendicular to the axis of the selective reduction
catalyst 6 flows axially of the selective reduction catalyst 6 through
turnabout, with the flow of the exhaust gas 3 directed outwardly of the
turning direction being suppressed by the depression 15 and that of the
exhaust gas directed inwardly of the turnabout being induced. As a
result, the tendency of the flow of relatively much exhaust gas 3 biased
outwardly of the turning direction is rectified to uniformiaze the
distribution of the exhaust gas 3 flow into the selective reduction
catalyst 6.

[0038] Moreover, especially in this embodiment, the depression 17 is
formed just in front of the curved portion constituted by the mixing pipe
16 and the exhaust inlet port 13 so as to guide the flow of the exhaust
gas 3 inwardly of the turning direction toward outward, so that even if
center-to-center distance between the mixing pipe 16 and the selective
reduction catalyst 6 is fixed and unchangeable from layout restrictions,
the depression 17 causes the portion of the exhaust passage inwardly of
the turning direction once directed outward at a position just in front
of the curved portion so that a curvature of the curved portion can be
reduced for alleviation of pace of curving, resulting in guidance of the
exhaust gas flow into the exhaust inlet port 13 in a smooth manner as
much as possible.

[0039] Thus, according to the above-mentioned embodiment, because of the
depression 15 formed on the introductory part 14, the exhaust gas 3 can
be introduced into the selective reduction catalyst 6 through the
turnabout with distribution of the flow of the exhaust gas 3 being
uniformized, so that the whole volume of the selective reduction catalyst
6 can be efficiently utilized for exertion of sufficient NOx
reduction effect, resulting in sufficient bringing-out of the exhaust
depuration ability of the selective reduction catalyst 6 to be inherently
exerted.

[0040] Moreover, formation of the depression 17 just in front of the
curved portion constituted by the mixing pipe 16 and the exhaust inlet
port 13 makes it possible to reduce the curvature of the curved portion
for alleviation of pace of curving and to guide the flow of the exhaust
gas 3 into the exhaust inlet port 13 with a smooth manner as much as
possible. As a result, the tendency of relatively much exhaust gas 3
biased outwardly of the turning direction can be further rectified and
substantial increase in pressure loss due to turnabout of the exhaust gas
3 can be prevented.

[0041] As in the present embodiment, especially in the case where the
selective reduction catalyst 6 using the urea water as the reduced
catalyst constitutes the post-treatment unit, meritoriously overcome are
the possibility that the misty urea water may collide against an inner
wall of the curved portion owing to increased pressure loss because of
the turnabout of the exhaust gas to induce the deposition of urea and the
possibility that arrangement of a dispersion plate on the inlet side of
the selective reduction catalyst 6 may cause the misty urea water to
collides against the dispersion plate to induce the deposition of urea.

[0042] It is to be understood that an exhaust emission control device
according to the invention is not limited to the above-mentioned
embodiment and that various changes and modifications may be made without
departing from the scope of the invention. For example, in the
illustration, the invention is applied to the inlet side of the selective
reduction catalyst in a case where the particulate filter is arranged in
parallel with the selective reduction catalyst; however, the invention
may be also similarly applicable to any post-treatment unit other than
the selective reduction catalyst. The invention may be also applicable to
exhaust emission control devices of various type with layouts using
turnabout of the exhaust gas into the post-treatment unit.